Abstract: Due to the fragile natural conditions, the capacity of stable production and sustainable production of farmland is weak in arid and semiarid regions of Northwest China. The second national land survey shows that there is a large amount of unstable farmland in Northwest China. However, the existing studies have not yet paid enough attention to the status and causes of unstable farmland. Especially, how to conduct unstable farmland conversion program and assess the subsequently potential impact is still a problem. Based on the data of national unstable farmland survey, this paper analyzes systematically the present situation and causes of unstable farmland in arid and semiarid regions of Northwest China. Further, this paper divides the ecological constraint intensity of unstable farmland into 3 classes by the aid of GIS (geographic information system) spatial analysis methods: high ecological constraint, middle ecological constraint and low ecological constraint, and set 3 farmland conversion scenarios including ecological protection scenario, comprehensive trade-off scenario and farmland protection scenario based on the different ecological constraint intensity to simulate land use change and the areas of farmland conversion before and after unstable farmland conversion program. Then this paper develops a primary feasibility assessment method of unstable farmland conversion in social, economic and ecological dimensions, and impacting level of grain yield, impacting level of income of farmer involved in unstable farmland and ecosystem service value are selected to represent social, economic and ecological impacts respectively. Taking Yuli County in Xinjiang Uygur Autonomous Region as the example, this paper assess the feasibility about the unstable farmland conversion based on the quantitative analysis results about the grain yield, income of farmer and ecosystem service value impacts brought by unstable farmland conversion program. The results show that there is 510021.53 hm2 unstable farmland in arid and semiarid regions of Northwest China that mainly locates in northern Xinjiang, central and eastern Gansu and central and southern Ningxia. As the land type is dominated by dry land and irrigated land as well as low-quality cultivated land, the utilization condition of unstable farmland is poor. If continuing to farming, 43.53% of unstable farmland in the region may affect regional ecological environment or be difficult to ensure stable harvest. The formation of unstable farmland in the region is mainly brought by desertification, accounting for 69.82% of unstable farmland. Over reclamations of the grassland, forest and continental river are also the causes for the unstable farmland. Unstable farmland conversion will result in the total grain output in Yuli County decreased by 28.64%, 20.35% and 10.43% respectively in 3 different scenarios. Although the short-run income of the farmers will be affected seriously due to unstable farmland conversion program, the long-run expected income brought by agricultural restructuring will compensate the loss of planting income, so the overall income of farmer will be increased by 10.41%, 12.01% and 15.25%, respectively. But if unstable farmland continues to farming, it will bring serious ecological impact. Unstable farmland conversion will improve the condition of regional ecological environment, and the ecosystem service value will increase by 26.74, 19.56 and 15.15 million yuan in 3 different scenarios respectively. Under the comprehensive balance, this paper thinks unstable farmland conversion program is feasible in Yuli County. Strict laws and regulations should be constituted to regulate the behavior of land reclamation in Northwest region, and local governments should properly handle the stock of unstable farmland and restrict the unstable farmland to continue to expand. At the same time, the regional functional zones and ecological red line control system should be promulgated as soon as possible, which can promote land use and ecological protection to achieve coordination.